class Base {
public:
    Base() : x_(0), y_(0.) {};
    Base(int x, double y) : x_(x), y_(y) {}
    Base(int x) : x_(x), y_(0.) {}
    Base(double y) : x_(0), y_(y) {}
private:
    int x_;
    double y_;
};

class Derived : public Base {
public:
    using Base::Base; // 引入积累的构造函数
};